1. Field of the Invention
This invention relates to apparatus for extrusion forming sheet products and, more particularly, to a system for selectively applying a coating to one or more sheet surfaces during sheet product formation.
2. Background Art
There is a multitude of different apparatus used to continuously form sheet products made up of one or more extrusion-formed sheet layers. In one exemplary apparatus, an extrusion assembly, through a sheet die, delivers flowable material to a nip/lamination location between adjacent and cooperating rolls on a roll stand assembly. The roll stand assembly may consist of separate sub-assemblies that cooperate to draw formed sheet layers in a downstream direction ultimately towards a point where the completed sheet product is appropriately handled, as by being packaged, staged, etc. One of the sub-assemblies is a roll stack sub-assembly made up of at least the aforementioned two rollers, defining the nip location, and potentially additional rolls that reroute the advancing sheet layer(s) during the sheet product formation. The other sub-assembly performs a sheet take-off function, exerting an advancing force upon the sheet layer(s).
It is also known to incorporate coating systems into such apparatus. In one exemplary form, a silicone liquid is applied to one or more of the exposed surfaces of the advancing sheet layer(s). This coating may be applied for different purposes. Silicone coatings are commonly used to perform an anti-static function. Silicone coatings are also commonly applied to facilitate separation of products that may be ultimately formed from the sheet product, such as cups or the like, which are nested/stacked, one within the other.
Typically, such apparatus are used in facilities wherein they do not have a dedicated function to form a single type of sheet product. The components on the apparatus are thus typically designed to allow a substantial degree of flexibility in terms of the nature of the material extruded, the number of sheet layers ultimately incorporated into the end product, and the thickness of any such layer(s). The end sheet product may consist of a single layer or multiple layers that are concurrently formed and/or combined continuously during the sheet product formation.
Designers of such apparatus focus not only on the system flexibility, but also on the cost and size of the apparatus. The apparatus, by their very nature, have a substantial footprint. Since manufacturing space is often limited in facilities where this equipment is employed, it is important to keep the apparatus footprint as small as is reasonably possible. As the footprint for the apparatus increases, so do the costs associated with the manufacture of the end product, that must ultimately be borne by the consumer.
Given the size and weight of the potentially multiple layers that are handled by such apparatus, the components of the apparatus by necessity are inherently robust and expensive. Thus, reduction in component number is always present as an objective for system designers, without compromising system reliability and flexibility.
Heretofore, coating systems have been incorporated into such apparatus as a series of dedicated components. Commonly, a coating system will be incorporated between the aforementioned rolls on the roll stack sub-assembly and a pair of cooperating rolls on the sheet take-off sub-assembly that produces the advancing force on the sheet layer(s). This construction, while effective in terms of operation, adds a considerable dimensional component to the overall apparatus, between the upstream and downstream ends thereof.
In one form, separate coating systems are serially combined with capabilities of coating different sides of an advancing sheet component. Again, while effective, this design may add significantly to both the overall cost of the apparatus and its dimension between the upstream and downstream ends thereof. Further, these additional systems may increase overall time invested in regular set-up, maintenance and ongoing repairs.
Additionally, the overall control of the apparatus may be complicated by requiring reprogramming of controls to coordinate the operation of the coating systems as different products are manufactured during separate runs.
In spite of the industry's continuing focus upon apparatus that can be constructed and operated efficiently from the standpoint of both equipment purchase cost and ongoing operation and maintenance, and that: a) have a great deal of flexibility in terms of the different products that can be produced therewith; b) can be set up and operated on a relatively small footprint; and c) can be reliably and safely operated, the industry has contended with a number of the above problems, and others, since there has been a lack of viable alternative structures that address the shortcomings in the prior art.